Mole or blue nevus: is it dangerous?

Blue nevus is a type of dermatological lesion that appears relatively frequently. It can take different shapes and sizes, but the most characteristic is the intense blue color that differentiates it a lot from other diseases.

While benign, the possibility of malignancy or confusion with a melanoma make evaluation by a dermatologist highly recommended. Want to know more? Keep reading!

How to identify it?

The preponderance of the blue nevus is greater in women, mainly in those of Asian race.

Although these lesions can appear anywhere on the body, they are more common in the extremities or the sacral coccygeal region. Sometimes they can be found extreme injuries to the head or mucosa that make diagnosis difficult.

From a clinical point of view, the characteristic finding of the blue nevus is its intense color. The shape can encompass various types of primary skin lesions, including macules (small and flat discoloration changes), papules (here, there is a small elevation and the content is solid) or nodules, among others.

In either case, the surface has a smooth texture and tends to be less than 1 centimeter, although "giant" lesions may also appear. Some patients can be born with the blue nevus, although the majority of cases are acquired from the third decade of life.

In these latter patients, the moles gradually increase in size over months or years until their growth stops abruptly.


The exact prevalence is unknown. There are approximate measurements that state that it affects more Asian people (3 to 5%) than Caucasians (0.5 to 4%), mainly women. Although it can affect all phototypes, it is more common in medium-toned skin (III and IV according to Fitzpatrick's classification).

According to other studies, it could occur in 1 in 3 000 live births, although it is an approximate figure that varies depending on the region under consideration.

Types of blue nevus

There is still no clear consensus regarding the classification of these injuries. However, in general terms, it is currently possible to distinguish the following forms:

  • Common or solitary.
  • Cell phone.
  • Compound.
  • Atypical.
  • Of large plates.

Despite the clinical differences, this diagnostic classification is applied in the field of histopathology. That is, when a mole biopsy is taken, it is pathologists who find microscopic changes and make the final diagnosis.

Exceptional cases

Sometimes it is possible to find moles with unusual clinical and histological characteristics. As usual, represent a diagnostic challenge, including during the analysis of the samples inside the microscope.

This case reported in 2009 is about a 7-year-old schoolboy, who was taken to the doctor for presenting repetitive episodes of rhinosinusal inflammation. During the physical examination, turbinate hypertrophy was found that, in part, could explain the pathology.

As part of the routine, an imaging study (computed tomography) was requested to verify the integrity of the paranasal sinuses. In this, important changes in the area corresponding to the left maxillary sinus, which under normal conditions, should have air.

To determine the origin, a more detailed examination was carried out, taking a sample of the lesion, which in fact had a hyperpigmented appearance (dark color). The sample was sent to the pathology laboratory for evaluation and then a blue nevus was reported. This is an example of a rare presentation of the disease.

Why can it happen?

LHistopathological findings suggest that blue nevi occur due to the presence of melanocytes in the dermis. These are cells capable of producing melanin, the main pigment in the skin. They tend to have strange shapes and are accompanied by changes in the surrounding tissue.

Everything seems to indicate that the cause of the blue nevus would be the combination of genetic and environmental factors. Through clinical investigations, G protein mutations have been determined, important molecules that participate in various biochemical reactions called "second messenger signals" in almost all cells of the body.

There is also evidence to suggest that the lesions are the product of embryological defects. The neural crest is a very small primitive structure rich in pluripotent stem cells.

These are capable of "transforming" into various tissues. At some point, these cells migrate to various places in the embryo to give rise to the nervous system and other structures, such as melanocytes.

Some of these cells may have migrated the wrong way, so they end up staying in the dermis and not in the epidermis (which is the most superficial layer of the skin and contains melanocytes). The typical blue coloration of lesions could be the result of a physical phenomenon called the Tyndall effect.

Blue nevi can occasionally appear in the context of other rare systemic syndromes. Such is the case of the Carney Complex, which is characterized by the appearance of myxomas, changes in skin pigmentation and hormonal problems, such as Cushing's syndrome.

When is it necessary to go to the doctor?

Although many dermatological lesions are benign and represent no more than a cosmetic discomfort for the patient, this is not always the case. One of the biggest challenges for dermatologists is early diagnosis and timely treatment of malignant lesions, especially melanoma.

This is the most common that can appear on the skin, and has a great capacity to metastasize and cause damage to other organs. From the pathophysiological point of view, it is characterized by uncontrolled proliferation of melanocytes, which gives it the characteristic dark color.

Unfortunately, it often goes unnoticed, even though there are easy to identify red flags. For this, anyone can use the classic A-B-C-D-E of melanomas:

  • Asymmetry: the lesion does not have a regular shape, so when dividing it into two halves using an imaginary line, differences in size can be found.
  • Edges: These tend to be uneven and not follow a well defined line.
  • Colour: tonality changes are frequent; this is the main reason why melanomas may mimic blue nevi.
  • Diameter: Although they are lesions that can start out very small, they increase in size very quickly and usually exceed 6 millimeters.
  • Evolution: they never have a static appearance. Over the months, they change in any of the aforementioned aspects.

Given the possibility that a simple blue nevus could actually be a malignant melanoma, it is necessary go to the dermatologist as soon as the lesion is detected.

Find out more: What is the ABCDE test for dermatology

Diagnosis of blue nevus

It is recommended to go to the doctor for an evaluation before the appearance of a mole with an unusual appearance.

When the dermatologist evaluates the lesions, there are two diagnostic phases. The first one is clinical. Through observation, the doctor will establish an initial suspicion. Afterwards, a biopsy will need to be taken for the pathologist to make the definitive diagnosis.

The clinical evaluation usually includes the performance of a dermoscopy, a vital tool for these specialists. It allows to see the lesions in greater detail by acting as a kind of magnifying glass, requiring an excellent light source to obtain more reliable results.

Thanks to this tool, it is possible to distinguish some characteristics that differentiate blue nevus from other benign or malignant lesions. This is achieved with different types of lighting, under which moles can reflect a different, easily detectable color.

Histopathologic confirmation is almost always necessary. The main findings were mentioned earlier and the diagnosis is generally not difficult to make. Depending on the results, the dermatologist may suggest different treatments.

Differential diagnostics

There are specific varieties of melanoma and other conditions that could be mistaken for blue nevus. Among them it is possible to point out the following

  • Dermatofibroma: it is a benign tumor with a hard consistency. It is often confused with a less common form of the blue nevus, known as the amelanocytic form.
  • Desmoplastic melanomaA rare variety that is usually diagnosed only by biopsy.

When is it important to remove it?

If the biopsy determines that it is a benign blue nevus, the injury may remain untreated. However, periodic medical evaluations are necessary, given the possibility that some subtypes of moles have to become malignant in the future.

In other cases, a more decisive treatment could be chosen, especially when there are aesthetic problems associated with psychological damage. For this, surgical excision is the most appropriate therapy.

The main problem with this treatment modality is that relapses of the disease may appear, in which the doctor could opt for a more conservative attitude. Sometimes the new growths can be accompanied by malignant lesions, and if that is the case, the treatment would be different.

Find out more: Treating skin cancer (melanoma)


In the vast majority of cases, because the lesions are benign, there are no associated complications. In some patients, the lesions can become malignant, so routine medical evaluation with the goal of early treatment is vital.

Fortunately, the blue nevus is benign in most cases. However, in those acquired cases where accelerated growth of the lesions is observed, it is advisable to go to the dermatologist who, in conjunction with the pathologist, will establish a definitive diagnosis.